The present invention relates to extreme ultraviolet (EUV) lithography, and more particularly, to contamination control and mitigation on EUV components.
Extreme ultraviolet lithography, which uses a source at 13.5 nm wavelength, is a promising technology for 0.1 micron integrated circuit (IC) fabrication. Since the absorption at that wavelength is very strong in all materials, EUV lithography employs Si/Mo multilayer mirrors and reflective masks as reflective optics, rather than refractive optics and through-the-mask reticles used in longer wavelength (optical) lithography. The strong absorption requires the use of reflective mask reticles, rather than through-the-mask reticles used in longer wavelength lithography. The EUV absorption also precludes the use of a pellicle to protect the reticle from particulate contamination.
There are many issues to be resolved in order to realize EUV lithography, such as, developing a powerful EUV source, robust components that direct the radiation (mirrors), and robust components that define the integrated circuit features (reticles). An EUV source with a collectable radiation power of 50 W to 150 W at over 5 kHz in the spectral range of 13-14 nm is required to achieve requirements for high volume manufacturing of 300 mm wafers. Laser-induced and electrical discharge gas plasma devices (EUV lamps) are under investigation as promising EUV sources. These sources generate EUV radiation by heating certain materials into a plasma to such a level, in the many 100,000""s C, that the material emits EUV radiation. Potential source materials which emit EUV radiation at excited energy levels include xenon, oxygen, and lithium.
FIG. 1 is a side view of an EUV reflective mask 10. The reflective mask and, similarly EUV mirror (not shown), comprises a quartz substrate 12 upon which is deposited a multilayer coating 14 of silicon (Si) and molybdenum (Mo). In addition, the reflective mask 10 has a highly detailed absorber pattern 16 deposited on top of the Si/Mo multilayer coating 14. A common absorber material is chrome. The reflective mask 10 is held to an electrostatic chuck 18 controlled by a chuck voltage 36. The EUV incoming radiation 32 impinges the reflective mask 10 at an angle and is reflected as outgoing radiation 33.
The EUV sources are emitters of high velocity particles 20. The high velocity particles 20 are a source of harmful contamination to the reflective surfaces 17 upon which they impinge and deposit. The Si/Mo multilayer mirrors and reflective masks 10, herein after referred to as reflective components 11, are highly sensitive to particle 20 contamination. Assuming the particles 20 are large enough, the contamination will result in the printing of a defect in every exposure field.
Several methods are used in an attempt to address particle 20 control on EUV reflective components 11. One method uses debris shields (not shown) through which the incoming EUV radiation 32 is passed to catch or filter the particles 20. But in the effort to maximize photon illumination, the xe2x80x9cmeshxe2x80x9d size has to be a compromise between particle 20 pass-through rate and reduction in EUV power.
Another method uses electrostatic fields for particle 20 control, which relies on the induced polarization created on the particle 20 by the presence of a strong electrostatic field. This leads to poor particle 20 removal of electrically neutral particles with low polarizability. Another method uses thermophoresis, which relies on the presence of a thermal gradient between the reflective surface 17 and the area above it. Thermophoresis is only marginally successful in the removal of larger particles 20 from a reflective surface 17.
None of these methods address the needs for preventing particulate contamination nor removing the particles 20 that do land on the reflective surfaces 17. Therefore, even with these processes, periodic manual cleaning is still required. But the delicate multilayer coatings 14 used in EUV reflective components 11 cannot withstand harsh or frequent cleaning.
In order for EUV lithography to meet commercial requirements and demands, including reliability, productivity, and maintenance, configurations and methods are needed for providing contamination control for the EUV mirrors and reflective masks without interference with the transmission of the radiation.